1. Technical Field
The present invention relates generally to a demapping technology for a Modified Dual Carrier Modulation (MDCM) scheme in a Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band (MB-OFDM UWB) system, and, more particularly, to a technology which enables the demapping of MDCM received signals to be performed using division and square root operations in the real number domain instead of complicated division and square root operations.
2. Description of the Related Art
With the expansion of the communication market and the advance of technology, research into wireless data communication is continuously expanding. In particular, the modulation and demodulation technology which is used in wireless data communication to modulate data into a transmittable and receivable form, to send the modulated signal, and to enable a reception unit to demodulate and analyze the modulated signal is being widely researched. The technology for maximizing the data rate by maximally utilizing a predetermined bandwidth is being researched.
Recently, with regard to wireless data communication technology, Ultra Wide Band (UWB) technology is being increasingly researched, along with Bluetooth. UWB technology is adapted to perform broadband data transmission and reception so as to transmit a large amount of data at ultrahigh speed, and is evaluated as having high utility in those fields requiring the transmission and reception of a large amount of data, such as the fields of high definition TV or home networking.
With regard to UWB technology, a Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band (MB-OFDM UWB) system is attracting attention as a technology which is capable of effectively using broad band in UWB technology. The above-described MB-OFDM UWB system is being widely researched because of its compatibility with other communication methods and capability to transmit and receive a large amount of data. In particular, in the MB-OFDM UWB system, research into the modulation and demodulation of data is considered to be important.
The MB-OFDM UWB system uses a Modified Dual Carrier Modulation (MDCM) scheme as the newest data modulation scheme. Research into demodulation at a receiving apparatus based on the modulation scheme and demapping used for the demodulation is being widely carried out. The MDCM scheme was proposed by WiMedia to support data transmission and reception at a data rate equal to or higher than 640 Mbps. In the MDCM scheme, modulation, that is, the creation of a transmission signal, is performed by creating data in the form of coordinate points each having predetermined complex coordinates.
FIG. 1 is a block diagram showing the configuration of a conventional MDCM scheme-based demapping device. Generally, in the MDCM scheme, a transmission signal is created using the following Equation:
                              (                                                                      d                  ⁡                                      [                    k                    ]                                                                                                                        d                  ⁡                                      [                                          k                      +                      50                                        ]                                                                                )                =                              (                                                            4                                                  1                                                                              1                                                                      -                    1                                                                        )                    ⁢                      (                                                                                x                    a                                                                                                                    x                    b                                                                        )                                              (        1        )            
xa, xb are complex numbers each of which has value I_out+j*Q_out which is determined based on an input bit string (for example, of 8 bits) and the following table.
TABLE 1Input bitsI-outQ-out0000−3−30001−3−10010−330011−310100−1−30101−1−10110−130111−1110003−310013−110103310113111001−311011−1111013111111
k is the index of a subcarrier. 50 pairs of (xa, xb) are received, and a total of 100 d[k]s (k=0˜99) are created using the above-described Equation and then transmitted in the form of a single OFDM symbol. d[k] and d[k+50] are complex numbers, and can be represented as dR[k]+j*dI[k] and dR[k+50]+j*dI[k+50], respectively. R denotes the real number part and I denotes the imaginary number part of the relevant complex number.
Since the transmission signal is converted into complex numbers using the above-described Equation, the transmission signal can be plotted at complex coordinates, and can be mapped to constellation points at the complex coordinates. Thereafter, a signal for the determined constellation points is transmitted, and a reception unit which has received the signal, in turn, can demap the signal and use the demapped signal as data by using a demodulation device.
The mapped transmission signal is influenced by a channel H[k] for each subcarrier, and a received signal r[k] is received by the reception unit based on the following Equation:r[k]=d[k]H[k]+N[k]  (2)
Here, H[k] denotes the channel of a k-th subcarrier, and N[k] denotes the noise signal of the k-th subcarrier. Accordingly, prior to demapping, a received signal which has been processed to detect only transmitted data should be created by preprocessing. In FIG. 1, an input signal modulated using an MDCM scheme passes through an Analog Digital Converter (ADC) and initial synchronization device 100 and a Fast Fourier Transform (FFT) circuit 101. The FFT circuit 101 converts the digital signal having passed through the ADC so that frequency and complex coordinate analysis can be performed thereon, and therefore only a signal, other than a noise signal, can be analyzed.
Thereafter, channel estimation for the received signal is performed (at a channel estimation unit 102). If the result of the channel estimation is HE[k] (estimated channel value)=CE_I+j*CE_Q, the received signal is multiplied by the conjugate complex number of the estimated channel value and then results are passed through the channel compensation unit 103 which performs channel compensation. Thereafter, the demapping device 104 multiplies constellation points for each subcarrier (in the embodiment of the present invention, 16 constellation points) by the absolute value of the channel. Then, the received signal is divided by the absolute value of the channel depending on the results of the channel estimation, the squares of the distances to the constellation points for each subcarrier are calculated, and then a soft decision for demapping is performed.
The channel compensation unit 103 compensates the received signal for the estimated channel HE[k] using the following Equations. If there is no error with the channel compensation unit 103, HE[k] becomes exactly equal to channel H[k], and the received signal also becomes rFDE[k] and rFDE[k+50].rFDE[k]=r[k]He*[k]=(d[k]H[k]+N[k])He*[k]˜|H[k]2 d[k]+Ne[k]rFDE[k+50]=r[k+50]He*[k+50]=(d[k+50]H[k+50]+N[k+50])He*[k+50]˜|H[k+50]|2 d[k+50]+Ne[k+50]  (3)
Thereafter, the demapping device 104 divides rFDE[k] and rFDE[k+50] by |H[k]| and |H[k+50]| to perform demapping, and then performs demapping. As a result, rmap[k] and the received signal rdemap[k] are calculated as follows:
                                              ⁢                                                            r                map                            ⁡                              [                k                ]                                      =                                                                                                  H                    ⁡                                          [                      k                      ]                                                                                        ⁢                                  d                  ⁡                                      [                    k                    ]                                                              +                                                                    N                    e                                    ⁡                                      [                    k                    ]                                                                                                          H                    ⁡                                          [                      k                      ]                                                                                                                      ⁢                                          ⁢                                          ⁢                                                    r                map                            ⁡                              [                                  k                  +                  50                                ]                                      =                                                                                                  H                    ⁡                                          [                                              k                        +                        50                                            ]                                                                                        ⁢                                  d                  ⁡                                      [                                          k                      +                      50                                        ]                                                              +                                                                    N                    e                                    ⁡                                      [                                          k                      +                      50                                        ]                                                                                                          H                    ⁡                                          [                                              k                        +                        50                                            ]                                                                                                                      ⁢                                          ⁢                                                    r                demap                            ⁡                              [                k                ]                                      =                                                                                                  H                    ⁡                                          [                      k                      ]                                                                                        ⁢                                                      d                    R                                    ⁡                                      [                    k                    ]                                                              +                                                                    N                    eR                                    ⁡                                      [                    k                    ]                                                                                                          H                    ⁡                                          [                      k                      ]                                                                                                    +                              j                ⁡                                  (                                                                                                                                      H                          ⁡                                                      [                                                          k                              +                              50                                                        ]                                                                                                                      ⁢                                                                        d                          R                                                ⁡                                                  [                                                      k                            +                            50                                                    ]                                                                                      =                                                                                            N                          eR                                                ⁡                                                  [                                                      k                            +                            50                                                    ]                                                                                                                                              H                          ⁡                                                      [                                                          k                              +                              50                                                        ]                                                                                                                                                        )                                                              ⁢                                          ⁢                                                    r                demap                            ⁡                              [                                  k                  +                  50                                ]                                      =                                                                                                  H                    ⁡                                          [                      k                      ]                                                                                        ⁢                                                      d                    I                                    ⁡                                      [                    k                    ]                                                              +                                                                    N                    eI                                    ⁡                                      [                    k                    ]                                                                                                          H                    ⁡                                          [                      k                      ]                                                                                                    +                              j                ⁡                                  (                                                                                                                                      H                          ⁡                                                      [                                                          k                              +                              50                                                        ]                                                                                                                      ⁢                                                                        d                          I                                                ⁡                                                  [                                                      k                            +                            50                                                    ]                                                                                      +                                                                                            N                          eI                                                ⁡                                                  [                                                      k                            +                            50                                                    ]                                                                                                                                              H                          ⁡                                                      [                                                          k                              +                              50                                                        ]                                                                                                                                                        )                                                                                        (        4        )            
Thereafter, the demapping step of calculating the squares of the distances between the received signal rdemap[k] and the constellation points, calculating a soft decision value based on the calculated squares of the distances and performing demapping is performed.
However, in the above-described conventional method, rdemap[k] and rdemap[k+50] must be calculated in order to calculate the above-described squares of the distances between the received signal rdemap[k] and the 16 constellation points, the channel-compensated received signals must be divided by |H[k]| and |H[k+50]| in order to calculate rdemap[k] and rdemap[k+50] as described above, and it is necessary to multiply a transmission constellation point by |H[k]| and |H[k+50]|. Furthermore, a square root operation is required in order to calculate |H[k]| and |H[k+50]|. Accordingly, in this case, accuracy, processing speed (for example, 528M samples/s) and the degree of complexity related to division and square root operations are important. In order to accurately distinguish the above-described 16 constellation points and perform the above-described operations for the 16 constellation points, accurate division and square root operations are required. As a result, the load of the demapping system itself is increased, and therefore complicated operations are required, so that problems related to speed and efficiency occur.